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1952 commer petrol sloper with crash gearbox


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Hi guys took my commer fire engine out over the weekend it has the cylinder petrol sloper engine with 4 speed crash gearbox, I'm really struggling coming bk down gears going up box is fine but really struggling 4th to 3rd 

And need to be at walking pace for 2nd gear 

I'm double declutching coming down box and blipping throttle a little to help things   along but still struggling 

Also what are your thoughts on fitting fully synthetic oil to gearbox 

So engine and gearbox speeds stay closer for longer 

I know this will open a can of worms but any help tips would be appreciated 

Cheers anton 

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We have a 1950 Commer 5 tonner with the same 6 cylinder slanted petrol engine. 

Cant say we have had the same problem with gear changing although saying that before she went out on the road we had the back axle jacked up and had to adjust the clutch pedal a lot to get gearchanges smoother.

The problem we have is she just keeps cooking up when out on a run. She is sat at the back of our shed now and because of COVID and no shows etc we havent felt the urgency to solve the problem.

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14 minutes ago, Anton, zil131 said:

Hi guys took my commer fire engine out over the weekend it has the cylinder petrol sloper engine with 4 speed crash gearbox, I'm really struggling coming bk down gears going up box is fine but really struggling 4th to 3rd 

And need to be at walking pace for 2nd gear 

I'm double declutching coming down box and blipping throttle a little to help things   along but still struggling 

Also what are your thoughts on fitting fully synthetic oil to gearbox 

So engine and gearbox speeds stay closer for longer 

I know this will open a can of worms but any help tips would be appreciated 

Cheers anton 

Hi Anton,

I suspect you are not slowing down enough before changing down. A common mistake if you are used to synchro boxes. It is a case of matching the speed of the gears and timing, takes practice but very satisfying when you master it. Keep at it but no need to force the gears in. Might be worth finding someone who is used to crash boxes to try your vehicle himself then teach you.

regards

Richard

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You say that you are having trouble changing down. Do you consider yourself experienced with crash boxes in trucks of this size ?

If not I suggest that blipping the throttle 'a little to help things' is not going to speed up the intput shaft of the gearbox enough to make a difference. The idea of double declutching on a downchange is to spin up the input side of the gearbox so that it is going at the same speed as it will be after the next gear is engaged. As everything naturally slows down as soon as you disengage the clutch when in neutral, you need to blip the engine quite a bit higher than it will be going in the next gear.

So, for down changes:

1  release throttle, press clutch, select neutral

2  Engage clutch, blip throttle to higher RPM than next gear will require.

3  Press clutch, engage next gear, open throttle, engage clutch.

For up changes there is usually no need to double clutch, just pause in neutral while the input shaft slows down.

As Richard says, you will find that both up and down shifts are much easier at lower revs. The engine has plenty of torque to keep you going.

David

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7 minutes ago, Richard Farrant said:

Hi Anton,

I suspect you are not slowing down enough before changing down. A common mistake if you are used to synchro boxes. It is a case of matching the speed of the gears and timing, takes practice but very satisfying when you master it. Keep at it but no need to force the gears in. Might be worth finding someone who is used to crash boxes to try your vehicle himself then teach you.

regards

Richard

I would agree with this.  I remember with embarrassment buying an ERF tractor unit, with a Fuller Eaton gearbox.  I drove away from the sellers' yard, and could not find one gear.   I spent the whole 50 mile journey in about two gears, using the range change switch in ways the designers never imagined.

Convinced I had bought a lemon I asked my mate Dodger (experienced in matters of crash gear boxes) to drive it and give a second opinion to my death sentence on the box.  He drove it faultlessly up and down the box.  Yikes.

It took some getting used to it, but I reckoned that a gear change was best effected very slowly.  Perhaps fitting in a few pages of a good book between changes.

 

 

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I past my army test on a 1953 3 ton Commer Q4 with crash box. Would always pick her to drive instead of the RL's with heaters she was great to drive. Once you have cracked it you can make her sing like a bird. Go out on a quite road and practice, you must get the speed off and match the engine speed or she will play you up. Mick

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Are you trying to change down to slow the truck instead of braking?
it works with a synchro box but not a crash box, there’s good advice in all of the above replies and practice makes perfect, gears for acceleration, brakes for slowing. 

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You mentioned about gearbox oil, just a thought,  has it got the right oil in it? I assume it’s EP but I made the mistake of putting EP90 in my GPW and to should have been straight 90. 

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I will say that ours took a bit of getting used to, and to change down you have to be travelling at quite a slow speed. Theres no rushing it.

I think the more you drive it you will find it easier. 

Going up with the Commer box is often quite pleasant. You hit it right and theres no need for double D. They really are nice trucks to drive.

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The point about not using an EP oil is that your box probably has bronze selector forks in it. EP additives eat into bronze and other yellow metals and the surface crumbles away. This is nothing to do with viscosity.

I would expect that your box requires straight 50 or 90 viscosity gear oil but I haven't got a book on it.

Going back to double clutching, it is entirely up to you to get the gears rotating at exactly the right speed so that they can engage. If you don't they simply won't go in and will do a lot of damage as they make that grating noise. Modern boxes do it for you, this one doesn't !

David

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9 minutes ago, David Herbert said:

The point about not using an EP oil is that your box probably has bronze selector forks in it. EP additives eat into bronze and other yellow metals and the surface crumbles away. This is nothing to do with viscosity.

Every day is a learning curve. 

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3 hours ago, Rootes75 said:

The recommended lubricant for the gearbox is 7 pints of 140 EP.

It is possible that it has steel selector forks but even then I find it very surprising that an EP oil was specified in a gearbox in 1952. Obviously though, if that is what the manual says then that is what you should use.

David

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Much good advice above about vehicle and engine speed when changing gear, but I would also add speed of actually moving the gear lever.

The Militant is much the same as yours, they can be a very unforgiving gearbox, miss time your change and you are doomed.

When I was first taught how to drive a Militant, the instructor suggested counting out the Army drill timing of 1-2-3-1 when changing gear.

Count 1, and move lever to neutral. Pause of 2-3 in neutral (while reving the engine for a down change) and then 1 again as you move the lever into the new gear.

He even had me shouting it out as I was doing it at first til I got the hang of it.

I taught our Stuart using the same method, he was a bit embarrassed initially, at the thought of shouting 1-23-1 while changing, but Militant is so noisy no one is going hear you.

Nowadays, after years of practice, I don't even use the clutch, just get the engine speed right and the gears just slide in. I still do the numbers in my head though

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51 minutes ago, Zero-Five-Two said:

I still do the numbers in my head though

It is funny the mnemonics one remembers.  I still have "brakes-legs-leads and clip" firmly planted in my brain for uncoupling a trailer and that was over twenty years ago I had that drummed into me to repeat like a parrot.

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Hi

Transmissions have individual personalities,  I have 3 CMPs all of them have the same 4 speed crash box transmissions, and each of them shift differently particularly shifting down through the gears.  The pause as you move to neutral,  the throttle blip, then the move to the next gear lower.  

Some of the problem I think comes not from the transmission but from the carburetor how quickly does the engine pick up.  One of my trucks doesn't like the cold and won't shift right until the transmission is warmed up, shifts up Ok but won't shift down easily until 10 or more miles.

As others have said if you are used to driving sycromesh transmission you will tend  try and shift to quickly.  Read the manual for the shift speeds put a little dot on glass of the speedometer.   Did this when I  was teaching my kids how to drive the trucks.  

There is also a driver relearning each spring after not having the trucks out on the road for several months.  

Cheers Phil 

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